1. Field of the Invention
The invention relates to an amplifier with an output transformer. The invention further relates to an output stage for use in such an amplifier. The invention further relates to a public address system comprising such an amplifier.
2. Description of the Related Art
Amplifiers are known in the art and are, for example, used as so-called PA amplifiers (Public Address amplifiers) in a Public Address System to send audio signals over long distances, for several different uses, such as, fire indicating installations, call installations, etc.
Such a system receives an audio signal at an input, and the PA amplifier supplies, via an output transformer, an audio signal with, for example, an output voltage of 100 Vrms over long distances to speakers having input transformers.
The known amplifier use a so-called H-bridge or Half H-bridge with four or two FETs, respectively.
A disadvantage of these known amplifiers is that the efficiency is less than 70%. A further disadvantage of these known amplifiers is that the output behavior in relation to noise is not good.
An object of the invention is to provide an amplifier not having the disadvantages of the prior art amplifiers. To this end an amplifier according to the invention comprises an input for receiving an input signal, an output for supplying an output signal, a comparator for converting the input signal into a pulse-width modulated signal, and a push-pull output stage comprising a first and a second switch and an output transformer having a primary winding coupled to the switches and a secondary winding coupled to the output of the push-pull amplifier, the output transformer further comprising a further secondary winding coupled to the comparator as a feedback loop.
The amplifier according to the invention is of the so-called push-pull type. Further, the amplifier comprises an output transformer, which is required in many Public Address Systems because the user requires a galvanic separation.
An extra secondary winding is used as a feedback connection.
In this way, a push-pull amplifier is obtained having a much higher efficiency than the prior art amplifiers, and uses a feedback loop for obtaining a stable amplifier.